How to use pgl.drawElement ?

Core Library Questions

fouchtre

in Core Library Questions • 10 months ago

Hello !

First of all, sorry if my english is not perfect, I'm from France and speak english approximately.

I'm new in Processing / OpenGL (I discovered it one month ago) but I'm good enough in ActionScript3 and have already done some projects based on GPU with FlashPlayer 11.

I'm trying to build a java library to "simulate" a Flash-project structure in Processing (with different kinds of displayObject / DisplayObjectContainer , customEvents , ...). I actually know how to do it easily with pushMatrix and popMatrix but what I really want to do is calculate all these stuffs inside a VertexShader.

My vertexShader works as expected with a single plane using pgl.drawArrays , but because I have no access to the 'IndexBuffer' (-> the buffer that registers the indices) with pgl.drawArray , I can't figure out how I can draw more than one "shape" in the same 'drawArrays' call.

I mean... If I undestand well (but maybe I don't) how works pgl.drawArrays , all the triangles must be interconnected , but I want to draw thousands of 'single plane' in the same 'draw call'.

I look around in the source code of PGL.java and found pgl.drawElements and I think that's what I want :)

But, obviously, there is a problem : drawElements needs 4 int arguments and no int[]. I guess it works like pgl. getAttribLocation but I don't find the good method... I searched a lot, found some stuff for processing 1.5 but nothing for processing 2...

Can someone help me ?

Thanks !

Replies(2)

fouchtre

Re: How to use pgl.drawElement ?

10 months ago

Maybe I'm not in a good direction...

In a perfect world, I would like to have a code similar to the "TextureQuad exemple" (in example/topic/texture) but with additional custom attributes that affect the vertexShader.

Is it possible to do it without using a "low level structure"?

Thanks !

fouchtre

Re: How to use pgl.drawElement ?

10 months ago

Hello All !

I'm far from my initial question but I found the solution I was looking for ! :)

It's actually possible to add custom attributes that affect Vertex & Fragment shader, and it's very easy to do !

Here is an exemple based on the 'TextureQuad' example :

import java.nio.*;
PImage img;
PShader testShader;
PGL pgl;
float[] scales;
float[] colors;
FloatBuffer scaleData;
FloatBuffer colorData;
int scaleLoc;
int colorLoc;
void setup() {
size(640, 360, P3D);
img = loadImage("Desert.jpg");
testShader = loadShader("fragment.glsl","vertex.glsl");
scales = new float[16];
scales[0] = scales[1] = scales[2] = scales[3] = scales[4] = scales[5] = scales[6] = scales[7] = scales[8] = scales[9] = scales[10] = scales[11] = scales[12] = scales[13] = scales[14] = scales[15] = 0.5;
colors = new float[16];
colors[0] = colors[4] = colors[8] = colors[12] = 1;
colors[1] = colors[5] = colors[9] = colors[13] = 0;
colors[2] = colors[6] = colors[10] = colors[14] = 0;
colors[3] = colors[7] = colors[11] = colors[15] = 1;
scaleData = allocateDirectFloatBuffer(16);
scaleData.put(scales);
scaleData.position(0);
colorData = allocateDirectFloatBuffer(16);
colorData.put(colors);
colorData.position(0);
noStroke();
}
void draw() {
background(0);
translate(width / 2, height / 2);
rotateY(map(mouseX, 0, width, -PI, PI));
rotateZ(PI/6);
pgl = beginPGL();
scaleLoc = pgl.getAttribLocation(testShader.glProgram, "inScale");
pgl.enableVertexAttribArray(scaleLoc);
pgl.vertexAttribPointer(scaleLoc, 4, PGL.FLOAT, false, 0, scaleData);
colorLoc = pgl.getAttribLocation(testShader.glProgram, "inColour");
pgl.enableVertexAttribArray(colorLoc);
pgl.vertexAttribPointer(colorLoc, 4, PGL.FLOAT, false, 0, colorData);
endPGL();
shader(testShader);
beginShape();
texture(img);
vertex(-100, -100, 0, 0, 0);
vertex(100, -100, 0, img.width, 0);
vertex(100, 100, 0, img.width, img.height);
vertex(-100, 100, 0, 0, img.height);
endShape();
resetShader();
}
FloatBuffer allocateDirectFloatBuffer(int n) {
return ByteBuffer.allocateDirect(n * Float.SIZE/8).order(ByteOrder.nativeOrder()).asFloatBuffer();
}

My vertexShader

uniform mat4 projmodelviewMatrix;
//custom attributes
attribute vec4 inScale;
attribute vec4 inColour; //inColor cannot be overrided (it always a white color)
//so I renamed it 'colour' for the test.
attribute vec4 inVertex;
attribute vec2 inTexcoord;
varying vec2 vertTexcoord;
varying vec4 vertColor;
void main() {
// Vertex in clip coordinates
vec4 pos = projmodelviewMatrix * inVertex;
pos.xy *= inScale.xy;
gl_Position = pos;
vertTexcoord = inTexcoord;
vertColor = inColour;
}

and my fragmentShader

#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif
uniform sampler2D textureSampler;
varying vec2 vertTexcoord;
varying vec4 vertColor;
void main() {
vec4 texture = texture2D(textureSampler, vertTexcoord);
texture.xyz *= vertColor.xyz;
gl_FragColor = texture;
}

The whole code draw a textured-colorTransformed-scaled quad.

It's much more easy than Flash, I'm impressed ! :)

EDIT : I have an error "OpenGL error 1281 at top endDraw(): invalid value" but all works fine. Other people already had these error but they didn't know why (all works fine for them too)